1. Field of the Invention
The present invention relates generally to variable gear ratio transmissions and, more particularly to novel pin configurations and differential shifting arrangements for variable gear ratio transmissions that utilize rings of moveable pins to vary drive ratios.
2. Description of the Related Art
Roughly 100 million bicycles are produced each year worldwide, and the gear-chain-derailleur system is the transmission used to move most all of them. An alternative concept appeared in the early 1980's when a different type of bicycle transmission system was proposed by Iseman in U.S. Pat. No. 4,457,739. In that system, individual rows of concentric metal pins in parallel discs were installed across or retracted from the gap between them using magnets and a linear slide device. The polarity of the magnets was used to shuttle pins on a given row across the slot between discs, effectively altering the diameter around which the bicycle drive chain passed and thereby the ratio between driven and driving entities. Later, unpatented designs by others moved away from magnetically actuated metal pins and towards mechanical manipulation of non-metallic pins for the transmission. Early designs with the non-metallic pins were inefficient, noisy and lacked the pin shuttling speed necessary to prevent pin head decapitations during pin manipulations. This shortfall was remedied by Lane in U.S. Ser. No. 12/267,098.
Testing of the design associated with U.S. Ser. No. 12/267,098 revealed a number of practical deficiencies, mostly associated with complexities in the shifting mechanism. It was discovered that: tight tolerances had to be held on various parts to affect a successful shift; the additional moving parts in the design created the need for greater shifting forces. Instituted design modifications altered the forces affecting pin movement, leading to an increase in pin binding and friction; and wear and noise remained practical concerns. The modified design also did not include options for the system load transfer component (the chain conveyance). Alternate shift actuation methods (e.g. mechanical cable versus electrical activation, etc.) were also not incorporated. These design considerations are addressed in the present disclosure. The new design is further intended for broader applications, well beyond use on bicycles.
U.S. Ser. Nos. 12/267,098, 10/301,901 and 09/620,184 represent early designs of the transmission system. These applications are incorporated herein as if they are fully rewritten.
The present invention provides an improved apparatus and method having benefits and characteristics not previously disclosed. The present invention utilizes less complex technology, yet it is a more reliable system for shift urging.